Metallic powder composition



Patented Sept. 19,1939 2,173,100

DIETALLIC POWDER COMPO SITION Joseph E. Drapeau, Jr., Calumet City, and James 0. Johnstone, Chicago, 111., ass'lgnors to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Application December 3, 1937, a

Serial No. 177,914 7 4 Claims. (Cl. 'I5-0.5)

This invention relates, to metallic Powder! Such differences in physical properties due to zoning, as are used for the producti n electrical but even more serious difllculties due to the forbrushes. por us b a ss a d sim a rt and mation of diil'erent alloys at dinerent zones in has particular reference to a new and novel comth sintering tion, Another important pound powder which displays the P y o not point is the difficulty with green growth. when se re tin w r y uniform metal distribution pressure is applied to metallic powder in the y be Obtained v111 the finished article- S order of twenty tonsper square inch, as is the case S ab e P op y being Obtained Without se-erlflcwith these moldings, and then released, there 8 e Other desirable Properties the DOWdeL is a tendenc to expansion, this increase in size e The invention also contemplates the control of being known as green growth. Other things m the app ren density 0! the metal p 9 being equal, large particle powder will give cifically. it co te p t e addition 01 y greater green growth than small particle powder;

r Sm quantities of thin liquids to these Powders so that segregation results not only in a slight t prev n segregation d n ra e n change in the dimensions of the molded object,

1.. to regulate the pp d ybut also in a change which is not entirely uniform.

In the manufacture of ca bon b the In the normal use of pure metal powders or called oil-less bea and Similar melded blends of metal powders and other. ingredients products, metallic powders are blended and com uch as carbon, graphite, etc., the apparent Dressed, With 0 Without r' Obtain the density, all other factors beings equal, plays an t sired molded ghiects- Var P y be important rolein the productlon'of equal weight used. pp lead, Z1110. carbon d graphite and size pressed metal powder objects such as being m nsth most mm These p w r bearings, bushings, rings, plates, brushes, eleceempl'ise Particles Varying Sizes; and e trical contact'points, etc. Up to the present time dlviduel Particles in any one powde v ry n S any changes in the apparent density of various a d app G y much as they y in lots or shipments of metal powder blends has these Particulars from vlmitilet 6 t e Other necessitated the operator to adjust the so-called p d s- W v ou d at even in n u well depth of the dle to compensate for variations compounded powdei', particles of micron or in apparent density. I

less diamete tend o dust D. d Separate m Another means of compensating for this variathe coa s Particles. This tendency is assration in apparent density has necessitated the in- 30 Voted W e e p e s of dlflel'eht Sorts e used; troducticn of complex weighing devices, thus enand it is particularly d where th nd is wit abling equal weight additions to the die in view or p wd s f considerably dlflerent a y d maintaining constant weight pressed metal diflerent mean particlesize, e. g. copper and tin. o t

f This ust d segregation Occurs to some eX- The general methods of apparent density content even in storage, but the tendency is asgratrol have been limited to the particle size and v ted considerably y m ic l r atm n such particle size distribution, and to the shape and as shaking, or mechanical conveying. porosity of the powdered material. For example,

In the manufacture of electrical brushes, where a solid spherical shape powder will have a greater conductivity and strength are of prime imporapparent density than porous spherical shape tance, the presence of segregated zones of coarse powder, all other factors being equal. Similarly,

and line material is particularly objectionable. an irregular shape particle size will not pack as This is particularly true since most brushes are closely as a spherical, cubic, etc., shaped particle compounded ofyarlous ingredients oi. varying of equal screen size or particle size distribution.

electrical conductivity, and of diiferent mean In attacking this problem of segregation, we

particle size; so that the zones difl'er not only in were faced with the further diillculty that any grain size, but also in chemical constitution. As solution to the problem preferably should not ala result, electrical conductivity varies in different fect the molding or other properties of the metalsections of the 'brush, and the tensile strength he powder. In particular, it is important, in

is of course that of the weakest zone. order to get satisfactory molding, that the powder 59 In the manufacture of powdered metal objects pour like a liquid; and it is common practice to such as bearings, the objections to segregation measure this flow of the powder by passing it are no less striking. These objects are generally through an orifice of restricted diameter, and made by compressing the blended powder in dies, determining the equivalent of viscosity in a liquid N and then slntering. Segregation not only gives by allowing a standard amount to flow through the standard orifice. In overcoming the tendency to segregate, in a satisfactory fashion, the flow must not be lost.

We have discovered that the tendency of the metallic powder to separate can be substantially overcome, and the apparent density regulated, without destroying the flow by incorporating with the powder a small amount of a liquid which has a viscosity no higher than that of S. A. E. #10 lubricating oil (about seconds Saybolt at F.). For overcoming the tendency to separate it has been found that percentages of liquids between 0.0025 and 0.03 are efiective in preventing segregation without stopping the flow. This same range also gives an effective control of the apparent density of the metal powder although if apparent density control is the only consideration, smaller amounts will result in a reduction in apparent density over the untreated powder. Likewise if in the apparent density control flow is not important, further reduction in apparent density may be obtained if desired, by addition of the liquid up to 0.05% and even up to 0.1%. Ordinarily, however, no more than 0.05% will be added and the preferred range for both segregation and apparent density control is between 0.0025 and 0.03% of liquid based on the powder.

Furthermore, we prefer to work with very thin liquids with viscosities of the order of kerosene, because as the viscosity increases, the ability to disperse throughout the mass lessens. With liquids whose viscosity is higher than that of #10' S. A. E. motor oil, the liquid will not disperse through the powder, but will ball the powder up locally, and destroy the flow without overcoming the tendency to segregation. Heavier liquids may be used only by blending with other liquids so that the actual liquid added is of sufliciently low viscosity.

Anotherqualification which-the liquid should possess is that it shall not react with the powder. For this reason, water, acids and unstable chlorinated hydrocarbons should not be used.

While volatile liquids such as benzol, petroleum, ether, etc., function eihcienly so long as they remain in the mass, their rapid evaporation takes them from the approved list. A slowly evaporating liquid such as kerosene, however, remains in the powder during storage, and evaporates from the molded article after manufacture; such a liquid is clearly preferable to a volatile liquid.

We have obtained elimination of segregation without loss of flow with volatile liquids like gasoline, benzol, petroleum ether, ethyl alcohol and ethyl acetate, with fixed liquids such as linseed oil, cottonseed oil and pine oil, and with slow evaporating liquids such as kerosene, petroleum naphtha and xylene, provided the amounts of liquid were kept low. Similar good results were obtained with a 50-50 blend of #20 S. A. E. lubricating oil and gasoline, the viscosity of the mixture being sufliciently low. It has been found preferable, however, to use a white mineral oil having a viscosity of #10 S. A. E. or less.

As an example of our invention, we blended 90 parts of a copper powder of a mean particle size of 30 microns diameter with 10 parts of a tin powder of 10 micron size. The mixture was flowed through an 0.075 inch diameter opening in a glass funnel similar in principle to the hour glass egg timing device. The funnel was fixed to a wooden frame in which a constant vibration was induced through a bell transformer, buzzer 'and rheostat set-up. The time required for 10 I Segregation 'lime of How Second: Blend straight Very marked 12 .0025 kerosene. Slight 20 .0050 kerosene. None. 40 .0075 korosene rl0 50 .01 kerosene do no 015 kerosene. .110. I00 .02 ker0scne "do .03 kerosene d0.... Nil

It will be observed from the above table that as little as .0025% addition of kerosene practically eliminated the tendency toward segregation and that above 0.03% there was a total loss of flow, and that for best results in both flow properties and prevention of segregation the amount should not be over 0.01%.

The above mixture, when made up into a bearing, had a considerably higher mechanical strength than a bearing similarly made from untreated powder.

A copper powder-carbon mixture, similarly treated with 0.01% kerosene, gave similar improved results over an untreated mixture.

The following example well illustrates how the apparent density of metal powders has been adjusted through this wetting with very small quantities of organic liquids. I

A batch of pure copper powder substantially all passing a 100 mesh sieve and approximately 55% passing a 325 mesh sieve with an apparent density as determined in the Scott Volumeter of 48.0 grams per cubic inch. The apparent density may be varied through a good wetting of this powder as follows through varied additions While we have shown but a few applications of our invention, it is applicable generally to the treatment of metal powders to reduce segregation and insure uniformity. We do not limit ourselves to the particular metal powders shown, but consider the invention to be applicable broadly to powdery mixes containing substantial percentages of any metal powders, with or without the presence of a non-metal such as carbon or the like.

This application is a continuation in part of application Serial No. 60,888, filed January 25, 1936.

We claim:

- 1. A substantially dry, non-segregating, freefiowing metal powder containing throughout a liquid non-reactive with the metal powder in a quantity about 0.0025 to 0.03% by weight.

2. A substantially dry non-segregating, freefiowing metal powder containing throughout a 4. The method of controlling the apparent density and of retarding the segregation of a metal powder which comprises predetermining the desired apparent density of the powder and incorporating throughout the powder an amount up to 0.1% of a liquid necessary to give the desired apparent density, said liquid being non-reactive with the powder, and having a viscosity no greater than #10 S. A. E. lubricating oil.

JOSEPH E. DRAPEAU, JR. JAMES O. JOHNSTONE. 

